//
//  kern_util.hpp
//  Lilu
//
//  Copyright © 2016-2017 vit9696. All rights reserved.
//

#ifndef kern_util_hpp
#define kern_util_hpp

#include <Headers/kern_config.hpp>
#include <Headers/kern_compat.hpp>

#include <libkern/libkern.h>
#include <libkern/c++/OSObject.h>
#include <libkern/OSDebug.h>
#include <mach/vm_types.h>
#include <mach/vm_prot.h>
#include <sys/proc.h>
#include <IOKit/IOLib.h>
#include <stdatomic.h>

#define xStringify(a) Stringify(a)
#define Stringify(a) #a

#define xConcat(a, b) Concat(a, b)
#define Concat(a, b) a ## b

/**
 *  Prefix name with your plugin name (to ease symbolication and avoid conflicts)
 */
#define ADDPR(a) xConcat(xConcat(PRODUCT_NAME, _), a)

/**
 *  Debugging state exported for your plugin
 */
extern bool ADDPR(debugEnabled);

/**
 *  Debugging print delay used as an ugly hack around printf bufferisation,
 *  which results in messages not appearing in the boot log.
 *  Use liludelay=1000 (1 second) boot-arg to put a second after each message.
 */
extern uint32_t ADDPR(debugPrintDelay);

/**
 *  Kernel version major
 */
extern const int version_major;

/**
 *  Kernel version minor
 */
extern const int version_minor;

/**
 *  Kernel map
 */
extern vm_map_t kernel_map;

/**
 *  Kernel proc
 */
extern proc_t kernproc;

/**
 *  For noreturn failures
 */
#define UNREACHABLE() do { __builtin_unreachable(); } while (0)

/**
 *  Conditional logging to system log prefixed with you plugin name
 *
 *  @param cond  precondition
 *  @param str   printf-like string
 */
#define SYSLOG_COND(cond, module, str, ...)                                                                			  \
	do {                                                                                                   			  \
	    if (cond)                                                                                          			  \
	        lilu_os_log( "%s%10s: @ " str "\n", xStringify(PRODUCT_NAME), safeString(module), ## __VA_ARGS__);		  \
	} while (0)

/**
 *  Write to system log prefixed with you plugin name
 *
 *  @param module log module
 *  @param str    printf-like string
 */
#define SYSLOG(module, str, ...) SYSLOG_COND(true, module, str, ## __VA_ARGS__)

/**
 *  Conditional tracing to system log prefixed with you plugin name
 *
 *  @param cond   precondition
 *  @param module log module
 *  @param str    printf-like string
 */
#define SYSTRACE_COND(cond, module, str, ...)                                                                        			 \
	do {                                                                                                             			 \
	    if (cond) {                                                                                                  			 \
	        SYSLOG(module, str, ## __VA_ARGS__);                                                                     			 \
		    OSReportWithBacktrace( "%s%10s: @ " str "\n", xStringify(PRODUCT_NAME), safeString(module), ## __VA_ARGS__);			 \
	    }                                                                                                            			 \
	} while (0)

/**
 *  Write call trace to system log prefixed with you plugin name
 *
 *  @param module log module
 *  @param str    printf-like string
 */
#define SYSTRACE(module, str, ...) SYSTRACE_COND(true, module, str, ## __VA_ARGS__)

/**
 *  Conditional panic prefixed with you plugin name
 *
 *  @param cond   precondition
 *  @param module log module
 *  @param str    printf-like string
 */
#define PANIC_COND(cond, module, str, ...)                                                             		\
	do {                                                                                               		\
	    if (cond) {                                                                                    		\
	        (panic)( "%s%10s: @ " str "\n", xStringify(PRODUCT_NAME), safeString(module), ## __VA_ARGS__);  \
	        UNREACHABLE();                                                                             		\
	    }                                                                                              		\
	} while (0)

/**
 *  Cause immediate kernel panic prefixed with you plugin name
 *
 *  @param module log module
 *  @param str    printf-like string
 */
#define PANIC(module, str, ...)  PANIC_COND(true, module, str, ## __VA_ARGS__)

#ifdef DEBUG

/**
 *  Conditional debug logging to system log prefixed with you plugin name
 *
 *  @param cond   precondition
 *  @param module log module
 *  @param str    printf-like string
 */
#define DBGLOG_COND(cond, module, str, ...)                                                     \
	do {                                                                                        \
	    SYSLOG_COND(ADDPR(debugEnabled) && (cond), module, "%s" str, "(DBG) ", ## __VA_ARGS__); \
	} while (0)

/**
 *  Write debug message to system log prefixed with you plugin name
 *
 *  @param module log module
 *  @param str    printf-like string
 */
#define DBGLOG(module, str, ...) DBGLOG_COND(true, module, str, ## __VA_ARGS__)

/**
 *  Conditional debug tracing to system log prefixed with you plugin name
 *
 *  @param cond   precondition
 *  @param module log module
 *  @param str    printf-like string
 */
#define DBGTRACE_COND(cond, module, str, ...)                                                     \
	do {                                                                                          \
	    SYSTRACE_COND(ADDPR(debugEnabled) && (cond), module, "%s" str, "(DBG) ", ## __VA_ARGS__); \
	} while (0)

/**
 *  Write debug call trace to system log prefixed with you plugin name
 *
 *  @param module log module
 *  @param str    printf-like string
 */
#define DBGTRACE(module, str, ...) DBGTRACE_COND(true, module, str, ## __VA_ARGS__)

#else /* DEBUG */

#define DBGLOG_COND(module, str, ...) do { } while (0)
#define DBGLOG(module, str, ...) do { } while (0)
#define DBGTRACE_COND(module, str, ...) do { } while (0)
#define DBGTRACE(module, str, ...) do { } while (0)

#endif

/**
 *  Macros to bypass kernel address printing protection
 */
#define PRIKADDR "0x%08X%08X"
#define CASTKADDR(x) \
	static_cast<uint32_t>(reinterpret_cast<uint64_t>(x) >> 32), \
	static_cast<uint32_t>(reinterpret_cast<uint64_t>(x))

/**
 *  Ugly floating point printing macros
 */
#define PRIFRAC "%lld.%04lld"
#define CASTFRAC(x) static_cast<int64_t>(x), static_cast<int64_t>(((x) - static_cast<int64_t>(x)) * 10000)

/**
 *  Macros to print the UUID
 */
#define PRIUUID "%02X%02X%02X%02X-%02X%02X-%02X%02X-%02X%02X-%02X%02X%02X%02X%02X%02X"
#define CASTUUID(uuid) \
	reinterpret_cast<const uint8_t *>(uuid)[0], \
	reinterpret_cast<const uint8_t *>(uuid)[1], \
	reinterpret_cast<const uint8_t *>(uuid)[2], \
	reinterpret_cast<const uint8_t *>(uuid)[3], \
	reinterpret_cast<const uint8_t *>(uuid)[4], \
	reinterpret_cast<const uint8_t *>(uuid)[5], \
	reinterpret_cast<const uint8_t *>(uuid)[6], \
	reinterpret_cast<const uint8_t *>(uuid)[7], \
	reinterpret_cast<const uint8_t *>(uuid)[8], \
	reinterpret_cast<const uint8_t *>(uuid)[9], \
	reinterpret_cast<const uint8_t *>(uuid)[10], \
	reinterpret_cast<const uint8_t *>(uuid)[11], \
	reinterpret_cast<const uint8_t *>(uuid)[12], \
	reinterpret_cast<const uint8_t *>(uuid)[13], \
	reinterpret_cast<const uint8_t *>(uuid)[14], \
	reinterpret_cast<const uint8_t *>(uuid)[15]

/**
 *  Export function or symbol for linking
 */
#define EXPORT __attribute__((visibility("default")))

/**
 *  Ensure the symbol is not exported
 */
#define PRIVATE __attribute__((visibility("hidden")))

/**
 *  For private fallback symbol definition
 */
#define WEAKFUNC __attribute__((weak))

/**
 *  Remove padding between fields
 */
#define PACKED __attribute__((packed))

/**
 *  Deprecate the interface
 */
#define DEPRECATE(x) __attribute__((deprecated(x)))

/**
 *  Non-null argument
 */
#define NONNULL __attribute__((nonnull))

/**
 *  Compiler hints regarding branching
 */
#define LIKELY(x) __builtin_expect(!!(x), 1)
#define UNLIKELY(x) __builtin_expect(!!(x), 0)

/**
 *  This function is supposed to workaround missing entries in the system log.
 *  By providing its own buffer for logging data.
 *
 *  @param format  formatted string
 */
EXPORT extern "C" void lilu_os_log(const char *format, ...) __printflike(1, 2);

/**
 *  Two-way substring search
 *
 *  @param stack    String to search in
 *  @param needle   Substring to search for
 *  @param len      Length of substring
 *
 *  @return substring address if there or nullptr
 */
EXPORT const char *strstr(const char *stack, const char *needle, size_t len=0);

/**
 *  Reverse character search
 *
 *  @param stack    String to search in
 *  @param ch       Character to search for
 *
 *  @return character address if there or null
 */
EXPORT char *strrchr(const char *stack, int ch);

/**
 *  XNU kernel implementation of a C-standard qsort function normally not exported by the kernel.
 *
 *  @param a    array to sort
 *  @param n    array length
 *  @param es   array element size
 *  @param cmp  array element comparator
 */
EXPORT void qsort(void *a, size_t n, size_t es, int (*cmp)(const void *, const void *));

/**
 *  Portable implementation of memmem function performing byte sequence (needle) search in another byte sequence (haystack).
 *
 *  @param h0    haystack
 *  @param k    haystack size
 *  @param n0   needle
 *  @param l  needle size
 *
 *  @return pointer to found sequence or NULL
 */
EXPORT void *lilu_os_memmem(const void *h0, size_t k, const void *n0, size_t l);

/**
 *  Portable implementation of memchr function performing byte search in a byte sequence.
 *
 *  @param src    source to search in
 *  @param c    byte to find
 *  @param n   source size in bytes
 *
 *  @return pointer to found byte or NULL
 */
EXPORT void *lilu_os_memchr(const void *src, int c, size_t n);

/**
 *  Count array elements
 *
 *  @param array   Array to process
 *
 *  @return number of elements
 */
template <class T, size_t N>
constexpr size_t arrsize(const T (&array)[N]) {
	return N;
}

/**
 *  C-style memory management from libkern, missing from headers
 */
extern "C" {
	void *kern_os_malloc(size_t size);
	void *kern_os_calloc(size_t num, size_t size);
	void kern_os_free(void *addr);
	void *kern_os_realloc(void *addr, size_t nsize);
	// kern_os_free does not check its argument for nullptr
	EXPORT void lilu_os_free(void *addr);
}

#if defined(__i386__)
/**
 *  ml_get_interrupts_enabled implementation as ml_get_interrupts_enabled is not exported on 10.5 or older
 */
inline bool lilu_get_interrupts_enabled() {
	uint32_t flags;

	__asm__ volatile ("pushf; pop	%0" :  "=r" (flags));
	return (flags & EFL_IF) != 0;
}

/**
 *  Wrapper around PE_parse_boot_arg as PE_parse_boot_argn is not exported in 10.4
 */
inline bool lilu_get_boot_args(const char *arg_string, void *arg_ptr, int max_len) {
	return PE_parse_boot_arg(arg_string, arg_ptr);
}

/**
 *  Implementation of strlcpy for 32-bit as strlcpy is not exported in 10.4
 */
EXPORT size_t lilu_strlcpy(char *dst, const char *src, size_t siz);

#elif defined(__x86_64__)
#define lilu_get_interrupts_enabled   ml_get_interrupts_enabled
#define lilu_get_boot_args            PE_parse_boot_argn
#define lilu_strlcpy                  strlcpy

#else
#error Unsupported arch.
#endif

/**
 *  Known kernel versions
 */
enum KernelVersion {
	Tiger         = 8,
	Leopard       = 9,
	SnowLeopard   = 10,
	Lion          = 11,
	MountainLion  = 12,
	Mavericks     = 13,
	Yosemite      = 14,
	ElCapitan     = 15,
	Sierra        = 16,
	HighSierra    = 17,
	Mojave        = 18,
	Catalina      = 19,
	BigSur        = 20,
	Monterey      = 21,
	Ventura       = 22,
};

/**
 *  Kernel minor version for symmetry
 */
using KernelMinorVersion = int;

/**
 *  Obtain major kernel version
 *
 *  @return numeric kernel version
 */
inline KernelVersion getKernelVersion() {
	return static_cast<KernelVersion>(version_major);
}

/**
 *  Obtain minor kernel version
 *
 *  @return numeric minor kernel version
 */
inline KernelMinorVersion getKernelMinorVersion() {
	return static_cast<KernelMinorVersion>(version_minor);
}

/**
 *  Check whether kernel boot argument is passed ignoring the value (e.g. -arg or arg).
 *
 *  @param name  argument name
 *
 *  @return true if argument was passed
 */
inline bool checkKernelArgument(const char *name) {
	int val[16];
	return lilu_get_boot_args(name, val, sizeof(val));
}

/**
 *  Parse apple version at compile time
 *
 *  @param version string literal representing apple version (e.g. 1.1.1)
 *
 *  @return numeric kernel version
 */
constexpr size_t parseModuleVersion(const char *version) {
	return (size_t)(version[0] - '0') * 100 + (version[2] - '0') * 10 + (version[4] - '0');
}

/**
 *  Access struct member by its offset
 *
 *  @param T     pointer to the field you need
 *  @param that  pointer to struct
 *  @param off   offset in bytes to the member
 *
 *  @return reference to the struct member
 */
template <typename T>
inline T &getMember(void *that, size_t off) {
	return *reinterpret_cast<T *>(static_cast<uint8_t *>(that) + off);
}

/**
 *  Align value by align (page size by default)
 *
 *  @param size  value
 *
 *  @return algined value
 */
template <typename T>
inline T alignValue(T size, T align = 4096) {
	return (size + align - 1) & (~(align - 1));
}

/**
 *  Check pointer alignment for type T
 *
 *  @param p  pointer
 *
 *  @return true if properly aligned
 */
template<typename T>
inline bool isAligned(T *p) {
	return reinterpret_cast<uintptr_t>(p) % alignof(T) == 0;
}

/**
 *  Obtain bit value of size sizeof(T)
 *  Warning, you are suggested to always pass the type explicitly!
 *
 *  @param n  bit no
 *
 *  @return bit value
 */
template <typename T>
constexpr T getBit(T n) {
	return static_cast<T>(1U) << n;
}

/**
 *  Obtain bit mask of size sizeof(T)
 *  Warning, you are suggested to always pass the type explicitly!
 *
 *  @param hi  starting high bit
 *  @param lo  ending low bit
 *
 *  @return bit mask
 */
template <typename T>
constexpr T getBitMask(T hi, T lo) {
	return (getBit(hi)|(getBit(hi)-1U)) & ~(getBit(lo)-1U);
}

/**
 *  Obtain bit field of size sizeof(T)
 *  Warning, you are suggested to always pass the type explicitly!
 *
 *  @param so  source
 *  @param hi  starting high bit
 *  @param lo  ending low bit
 *
 *  @return bit field value
 */
template <typename T>
constexpr T getBitField(T so, T hi, T lo) {
	return (so & getBitMask(hi, lo)) >> lo;
}

/**
 *  Set bit field of size sizeof(T)
 *  Warning, you are suggested to always pass the type explicitly!
 *
 *  @param va  value
 *  @param hi  starting high bit
 *  @param lo  ending low bit
 *
 *  @return bit field value
 */
template <typename T>
constexpr T setBitField(T so, T hi, T lo) {
	return (so << lo) & getBitMask(hi, lo);
}

/**
 *  This is an ugly replacement to std::find_if, allowing you
 *  to check whether a container consists only of value values.
 *
 *  @param in     container
 *  @param size   container size
 *  @param value  value to look for
 *
 *  @return true if an element different from value was found
 */
template <typename T, typename Y>
inline bool findNotEquals(T &in, size_t size, Y value) {
	for (size_t i = 0; i < size; i++)
		if (in[i] != value)
			return true;
	return false;
}

/**
 *  Returns non-null string when they can be null
 *
 *  @param str  original string
 *
 *  @return non-null string
 */
inline const char *safeString(const char *str) {
	return str ? str : "(null)";
}

/**
 *  A shorter form of writing reinterpret_cast<decltype(&org)>(ptr)
 */
template <typename T>
inline T FunctionCast(T org, mach_vm_address_t ptr) {
	return reinterpret_cast<T>(ptr);
}

/**
 *  Reference cleaner
 */
template<class T> struct remove_reference      {typedef T type;};
template<class T> struct remove_reference<T&>  {typedef T type;};
template<class T> struct remove_reference<T&&> {typedef T type;};


/**
 *  Typed buffer allocator
 */
namespace Buffer {
	/**
	 *  Allocating more than 1 GB is unreasonable for stability purposes.
	 */
	static constexpr size_t BufferMax = 1024*1024*1024;

	template <typename T>
	inline T *create(size_t size) {
		size_t s = sizeof(T) * size;
		if (s > BufferMax) return nullptr;
		return static_cast<T *>(kern_os_malloc(s));
	}

	template <typename T>
	inline bool resize(T *&buf, size_t size) {
		size_t s = sizeof(T) * size;
		if (s > BufferMax) return false;
		auto nbuf = static_cast<T *>(kern_os_realloc(buf, s));
		if (nbuf) {
			buf = nbuf;
			return true;
		}

		return false;
	}

	template <typename T>
	inline void deleter(T *buf NONNULL) {
		lilu_os_free(buf);
	}
}

/**
 *  Dynamically allocated page
 */
struct Page {
	/**
	 *  Allocates a page
	 *
	 *  @return true on success
	 */
	EXPORT bool alloc();

	/**
	 *  Sets page protection
	 *
	 *  @param prot protection bitmask
	 *
	 *  @return true on success
	 */
	EXPORT bool protect(vm_prot_t prot);

	/**
	 *  Deletes the page
	 *
	 *  @param p page
	 */
	EXPORT static void deleter(Page *p NONNULL);

	/**
	 *  Creates a page object
	 *
	 *  @return pointer to new page object or nullptr
	 */
	EXPORT static Page *create();

	/**
	 *  Page buffer
	 */
	uint8_t *p {nullptr};
};

/**
 *  Thread specific container of T values in up to N threads
 */
template <typename T, size_t N>
class ThreadLocal {
	/**
	 *  A list of tread identifiers
	 */
	_Atomic(thread_t) threads[N] {};

	/**
	 *  A list of value references
	 */
	T values[N] {};

public:
	/**
	 *  Initialise storage
	 */
	void init() {}

	/**
	 *  Deinitialise storage
	 */
	void deinit() {
		for (size_t i = 0; i < N; i++) {
			atomic_store_explicit(&threads[i], nullptr, memory_order_relaxed);
			values[i] = {};
		}
	}

	/**
	 *  Set or overwrite thread specific value
	 *
	 *  @param value  value to store
	 *
	 *  @return true on success
	 */
	bool set(T value) {
		auto currThread = current_thread();
		T *ptr = nullptr;

		// Find previous value if any
		for (size_t i = 0; ptr == nullptr && i < N; i++)
			if (atomic_load_explicit(&threads[i], memory_order_acquire) == currThread)
				ptr = &values[i];

		// Find null value if any
		for (size_t i = 0; ptr == nullptr && i < N; i++) {
			thread_t nullThread = nullptr;
			if (atomic_compare_exchange_strong_explicit(&threads[i], &nullThread, currThread,
				memory_order_acq_rel, memory_order_acq_rel))
				ptr = &values[i];
		}

		// Insert if we can
		if (ptr) *ptr = value;

		return ptr != nullptr;
	}

	/**
	 *  Get thread specific value
	 *
	 *  @return pointer to stored value on success
	 */
	T *get() {
		auto currThread = current_thread();

		for (size_t i = 0; i < N; i++)
			if (atomic_load_explicit(&threads[i], memory_order_acquire) == currThread)
				return &values[i];

		return nullptr;
	}

	/**
	 *  Unset thread specific value if present
	 *
	 *  @return true on success
	 */
	bool erase() {
		auto currThread = current_thread();

		for (size_t i = 0; i < N; i++) {
			if (atomic_load_explicit(&threads[i], memory_order_acquire) == currThread) {
				values[i] = {};
				thread_t nullThread = nullptr;
				return atomic_compare_exchange_strong_explicit(&threads[i], &currThread,
					nullThread, memory_order_acq_rel, memory_order_acq_rel);
			}
		}

		return false;
	}
};

/**
 *  Use this deleter when storing scalar types
 */
template <typename T>
static void emptyDeleter(T) { /* no dynamic alloc */ }

template <typename T, typename Y, void (*deleterT)(T)=emptyDeleter<T>, void (*deleterY)(Y)=emptyDeleter<Y>>
struct ppair {
	T first;
	Y second;

	static ppair *create() {
		return new ppair;
	}

	static void deleter(ppair *p NONNULL) {
		deleterT(p->first);
		deleterY(p->second);
		delete p;
	}
};

/**
 *  Embedded vector-like container
 *  You must call deinit before destruction
 *  Ugh, someone, please, port libc++ to XNU...
 *
 *  @param T        held type
 *  @param P        destructible type
 *  @param deleter  type destructor
 */
template <typename T, typename P, void (*deleter)(P)=emptyDeleter<P>>
class evector_base {
	T *ptr {nullptr};
	size_t cnt {0};
	size_t rsvd {0};
public:
	/**
	 *  Return evector size
	 *
	 *  @return element count
	 */
	size_t size() const {
		return cnt;
	}

	/**
	 *  Return pointer to the elements
	 *  Valid until evector contents change
	 *
	 *  @return elements ptr
	 */
	T *data() const {
		return ptr;
	}

	/**
	 *  Return last element id
	 *
	 *  @return element id
	 */
	size_t last() const {
		return cnt-1;
	}

	/**
	 *  Return evector element reference
	 *
	 *  @param index array index
	 *
	 *  @return the element at provided index
	 */
	T &operator [](size_t index) {
		return ptr[index];
	}

	/**
	 *  Return evector const element reference
	 *
	 *  @param index array index
	 *
	 *  @return the element at provided index
	 */
	const T &operator [](size_t index) const {
		return ptr[index];
	}

	/**
	 *  Reserve memory for at least N elements
	 *
	 *  @param num  amount of elements
	 *
	 *  @return elements ptr or null
	 */
	template <size_t MUL = 1>
	T *reserve(size_t num) {
		if (rsvd < num) {
			T *nPtr = static_cast<T *>(kern_os_realloc(ptr, MUL * num * sizeof(T)));
			if (nPtr) {
				ptr = nPtr;
				rsvd = MUL * num;
			} else {
				return nullptr;
			}
		}

		return ptr;
	}

	/**
	 *  Erase evector element
	 *
	 *  @param index element index
	 */
	void erase(size_t index, bool free=true) {
		deleter(ptr[index]);
		if (--cnt != index)
			lilu_os_memmove(&ptr[index], &ptr[index + 1], (cnt - index) * sizeof(T));

		if (free && cnt == 0) {
			kern_os_free(ptr);
			ptr = nullptr;
			rsvd = 0;
		}
	}

	/**
	 *  Add an element to evector end
	 *
	 *  @param &element an element to add
	 *
	 *  @return true on success
	 */
	template <size_t MUL = 1>
	bool push_back(T &element) {
		if (reserve<MUL>(cnt+1)) {
			ptr[cnt] = element;
			cnt++;
			return true;
		}

		SYSLOG("evector", "insertion failure");
		return false;
	}

	/**
	 *  Add an element to evector end
	 *
	 *  @param &element an element to add
	 *
	 *  @return true on success
	 */
	template <size_t MUL = 1>
	bool push_back(T &&element) {
		if (reserve<MUL>(cnt+1)) {
			ptr[cnt] = element;
			cnt++;
			return true;
		}

		SYSLOG("evector", "insertion failure");
		return false;
	}

	evector_base() = default;
	evector_base(const evector_base &) = delete;
	evector_base operator =(const evector_base &) = delete;

	/**
	 * Free the used memory
	 */
	void deinit() {
		if (ptr) {
			for (size_t i = 0; i < cnt; i++)
				deleter(ptr[i]);
			kern_os_free(ptr);
			ptr = nullptr;
			cnt = rsvd = 0;
		}
	}
};

/**
*  Embedded vector-like container, simplified specialisation
*  You must call deinit before destruction
*
*  @param T        held type
*  @param deleter  type destructor
*/
template <typename T, void (*deleter)(T)=emptyDeleter<T>>
class evector : public evector_base<typename remove_reference<T>::type, T, deleter> { };

/**
 *  Represents a circular buffer protected by a recursive mutex lock
 */
template <typename T>
struct CircularBuffer {
private:
	/**
	 *  The internal storage
	 */
	T *storage {nullptr};
	
	/**
	 *  The buffer capacity
	 */
	IOItemCount size {0};
	
	/**
	 *  The current index for the next read operation
	 */
	IOItemCount indexr {0};
	
	/**
	 *  The current index for the next write operation
	 */
	IOItemCount indexw {0};
	
	/**
	 *  The current number of elements in the buffer
	 */
	IOItemCount count {0};
	
	/**
	 *  The recursive mutex lock that protects the buffer
	 */
	IORecursiveLock *lock {nullptr};
	
public:
	/**
	 *  Initialize a circular buffer
	 *
	 *  @param buffer A non-null storage buffer
	 *  @param capacity The total number of elements
	 *  @return `true` on success, `false` otherwise.
	 *  @warning The caller is responsbile for managing the lifecycle of the given storage buffer.
	 */
	bool init(T *buffer, IOItemCount capacity) {
		storage = buffer;
		size = capacity;
		lock = IORecursiveLockAlloc();
		return lock != nullptr;
	}
	
	/**
	 *  Initialize a circular buffer
	 *
	 *  @param storage A storage buffer
	 *  @return `true` on success, `false` otherwise.
	 *  @warning The caller is responsbile for managing the lifecycle of the given storage buffer.
	 */
	template <size_t N>
	bool init(T (&storage)[N]) {
		return init(storage, N);
	}
	
	/**
	 *  Deinitialize the circular buffer
	 */
	void deinit() {
		IORecursiveLockFree(lock);
	}
	
	/**
	 *  Create a circular buffer with the given capacity
	 *
	 *  @param size The total number of elements
	 *  @return A non-null instance on success, `nullptr` if no memory.
	 *  @warning The caller must invoke `CircularBuffer::destory()` to release the returned buffer.
	 */
	static CircularBuffer<T> *withCapacity(IOItemCount size) {
		auto storage = Buffer::create<T>(size);
		if (storage == nullptr)
			return nullptr;
		
		auto instance = new CircularBuffer<T>();
		if (instance == nullptr) {
			Buffer::deleter(storage);
			return nullptr;
		}
		
		if (!instance->init(storage, size)) {
			delete instance;
			Buffer::deleter(storage);
			return nullptr;
		}
		
		return instance;
	}
	
	/**
	 *  Destroy the given circular buffer
	 *
	 *  @param buffer A non-null circular buffer returned by `CircularBuffer::withCapacity()`.
	 */
	static void deleter(CircularBuffer<T> *buffer NONNULL) {
		Buffer::deleter(buffer->storage);
		buffer->deinit();
		delete buffer;
	}
	
	/**
	 *  Destory the given circular buffer if it is non-null and set it to nullptr
	 *
	 *  @param buffer A nullable circular buffer returned by `CircularBuffer::withCapacity()`.
	 *  @note This function mimics the macro `OSSafeReleaseNULL()`.
	 */
	static void safeDeleter(CircularBuffer<T> *&buffer) {
		if (buffer != nullptr) {
			deleter(buffer);
			buffer = nullptr;
		}
	}
	
	/**
	 *  Check whether the circular buffer is empty
	 *
	 *  @return `true` if the buffer is empty, `false` otherwise.
	 */
	bool isEmpty() {
		IORecursiveLockLock(lock);
		bool retVal = (count == 0) && (indexr == indexw);
		IORecursiveLockUnlock(lock);
		return retVal;
	}
	
	/**
	 *  Check whether the circular buffer is full
	 *
	 *  @return `true` if the buffer is full, `false` otherwise.
	 */
	bool isFull() {
		IORecursiveLockLock(lock);
		bool retVal = (count == size) && (indexr == indexw);
		IORecursiveLockUnlock(lock);
		return retVal;
	}
	
	/**
	 *  Get the number of elements in the circular buffer
	 *
	 *  @return The current number of elements in the buffer.
	 */
	IOItemCount getCount() {
		IORecursiveLockLock(lock);
		IOItemCount retVal = count;
		IORecursiveLockUnlock(lock);
		return retVal;
	}
	
	/**
	 *  Write the given element to the circular buffer
	 *
	 *  @param element The element to write
	 *  @return `true` on success, `false` if the buffer is full.
	 */
	bool push(const T &element) {
		IORecursiveLockLock(lock);
		if (isFull()) {
			IORecursiveLockUnlock(lock);
			return false;
		}
		storage[indexw] = element;
		indexw += 1;
		indexw %= size;
		count += 1;
		IORecursiveLockUnlock(lock);
		return true;
	}
	
	/**
	 *  Read the next element from the circular buffer
	 *
	 *  @param element The element read from the buffer
	 *  @return `true` on success, `false` if the buffer is empty.
	 */
	bool pop(T& element) {
		IORecursiveLockLock(lock);
		if (isEmpty()) {
			IORecursiveLockUnlock(lock);
			return false;
		}
		element = storage[indexr];
		indexr += 1;
		indexr %= size;
		count -= 1;
		IORecursiveLockUnlock(lock);
		return true;
	}
};

/**
 *  Wrap an object that is not an instance of OSObject
 */
class EXPORT OSObjectWrapper: public OSObject {
	/**
	 *  Constructors & Destructors
	 */
	OSDeclareDefaultStructors(OSObjectWrapper);
	
	using super = OSObject;
	
	/**
	 *  Wrapped object
	 */
	void *object {nullptr};
	
public:
	/**
	 *  Initialize the wrapper with the given object
	 *
	 *  @param object The wrapped object that is not an `OSObject`
	 *  @return `true` on success, `false` otherwise.
	 */
	EXPORT bool init(void *object);
	
	/**
	 *  Reinterpret the wrapped object as the given type
	 *
	 *  @return The wrapped object of the given type.
	 */
	template <typename T>
	T *get() {
		return reinterpret_cast<T *>(object);
	}
	
	/**
	 *  Create a wrapper for the given object that is not an `OSObject`
	 *
	 *  @param object A non-null object
	 *  @return A non-null wrapper on success, `nullptr` otherwise.
	 *  @warning The caller is responsbile for managing the lifecycle of the given object.
	 */
	EXPORT static OSObjectWrapper *with(void *object);
};

namespace Value {
	template <typename T>
	struct Value {
		const T &value;

		explicit Value(const T &value) : value(value) {}

	#if __cplusplus >= 201703L
		// Available as of C++17
		template<typename... Ts>
		bool isOneOf(const Ts&... args) {
			return ((value == args) || ...);
		}

		// Available as of C++17
		template <typename... Ts>
		bool isNotOneOf(const Ts&... args) {
			return ((value != args) && ...);
		}
	#endif
	};
	
	template <typename T>
	static Value<T> of(const T &value) {
		return Value<T>(value);
	}
}

#endif /* kern_util_hpp */
